setdisplay(256,192,32,1):paper(0xFFFFFF):ink(0):pen(0):cls
for f=0 to 125 step 10
g=80-f*80*125
line(f,80,125,g)
line(125,g,250-f,80)
line(f,80,125,160-g)
line(125,160-g,250-f,80)
next
waitkey